There are four objectives in this proposal: 1) Calculate the ratio of nexal membrane to plasma membrane with an automated planimeter from freeze fracture replicas of earthworm median giant axon septa. 2) Calculate nexal membrane permeability to various radioactive molecules such as carbon labelled cyclic AMP with radioautography and densitometric techniques. 3) Use freeze fracture and physiological parameters such as the coupling ratio and fluorescent diffusion through the earthworm septa to determine if the morphological changes observed in nexuses with lanthanum treatment are responsible for physiological uncoupling. 4) Determine the effect of lanthanoids and other polyvalent cations such as iron and calcium on the structure of ABRM nexuses.